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Diffstat (limited to 'src/dbinc/atomic.h')
| -rw-r--r-- | src/dbinc/atomic.h | 220 |
1 files changed, 220 insertions, 0 deletions
diff --git a/src/dbinc/atomic.h b/src/dbinc/atomic.h new file mode 100644 index 00000000..096176a5 --- /dev/null +++ b/src/dbinc/atomic.h @@ -0,0 +1,220 @@ +/* + * See the file LICENSE for redistribution information. + * + * Copyright (c) 2009, 2012 Oracle and/or its affiliates. All rights reserved. + * + * $Id$ + */ + +#ifndef _DB_ATOMIC_H_ +#define _DB_ATOMIC_H_ + +#if defined(__cplusplus) +extern "C" { +#endif + +/* + * Atomic operation support for Oracle Berkeley DB + * + * HAVE_ATOMIC_SUPPORT configures whether to use the assembly language + * or system calls to perform: + * + * atomic_inc(env, valueptr) + * Adds 1 to the db_atomic_t value, returning the new value. + * + * atomic_dec(env, valueptr) + * Subtracts 1 from the db_atomic_t value, returning the new value. + * + * atomic_compare_exchange(env, valueptr, oldval, newval) + * If the db_atomic_t's value is still oldval, set it to newval. + * It returns 1 for success or 0 for failure. + * + * The ENV * parameter is used only when HAVE_ATOMIC_SUPPORT is undefined. + * + * If the platform does not natively support any one of these operations, + * then atomic operations will be emulated with this sequence: + * MUTEX_LOCK() + * <op> + * MUTEX_UNLOCK(); + * Uses where mutexes are not available (e.g. the environment has not yet + * attached to the mutex region) must be avoided. + */ +#if defined(DB_WIN32) +typedef DWORD atomic_value_t; +#else +typedef int32_t atomic_value_t; +#endif + +/* + * Windows CE has strange issues using the Interlocked APIs with variables + * stored in shared memory. It seems like the page needs to have been written + * prior to the API working as expected. Work around this by allocating an + * additional 32-bit value that can be harmlessly written for each value + * used in Interlocked instructions. + */ +#if defined(DB_WINCE) +typedef struct { + volatile atomic_value_t value; + volatile atomic_value_t dummy; +} db_atomic_t; +#else +typedef struct { + volatile atomic_value_t value; +} db_atomic_t; +#endif + +/* + * These macro hide the db_atomic_t structure layout and help detect + * non-atomic_t actual argument to the atomic_xxx() calls. DB requires + * aligned 32-bit reads to be atomic even outside of explicit 'atomic' calls. + * These have no memory barriers; the caller must include them when necessary. + */ +#define atomic_read(p) ((p)->value) +#define atomic_init(p, val) ((p)->value = (val)) + +#ifdef HAVE_ATOMIC_SUPPORT + +#if defined(DB_WIN32) +#if defined(DB_WINCE) +#define WINCE_ATOMIC_MAGIC(p) \ + /* \ + * Memory mapped regions on Windows CE cause problems with \ + * InterlockedXXX calls. Each page in a mapped region needs to \ + * have been written to prior to an InterlockedXXX call, or the \ + * InterlockedXXX call hangs. This does not seem to be \ + * documented anywhere. For now, read/write a non-critical \ + * piece of memory from the shared region prior to attempting \ + * shared region prior to attempting an InterlockedExchange \ + * InterlockedXXX operation. \ + */ \ + (p)->dummy = 0 +#else +#define WINCE_ATOMIC_MAGIC(p) 0 +#endif + +#if defined(DB_WINCE) || (defined(_MSC_VER) && _MSC_VER < 1300) +/* + * The Interlocked instructions on Windows CE have different parameter + * definitions. The parameters lost their 'volatile' qualifier, + * cast it away, to avoid compiler warnings. + * These definitions should match those in dbinc/mutex_int.h for tsl_t, except + * that the WINCE version drops the volatile qualifier. + */ +typedef PLONG interlocked_val; +#define atomic_inc(env, p) \ + (WINCE_ATOMIC_MAGIC(p), \ + InterlockedIncrement((interlocked_val)(&(p)->value))) + +#else +typedef LONG volatile *interlocked_val; +#define atomic_inc(env, p) \ + InterlockedIncrement((interlocked_val)(&(p)->value)) +#endif + +#define atomic_dec(env, p) \ + (WINCE_ATOMIC_MAGIC(p), \ + InterlockedDecrement((interlocked_val)(&(p)->value))) +#if defined(_MSC_VER) && _MSC_VER < 1300 +#define atomic_compare_exchange(env, p, oldval, newval) \ + (WINCE_ATOMIC_MAGIC(p), \ + (InterlockedCompareExchange((PVOID *)(&(p)->value), \ + (PVOID)(newval), (PVOID)(oldval)) == (PVOID)(oldval))) +#else +#define atomic_compare_exchange(env, p, oldval, newval) \ + (WINCE_ATOMIC_MAGIC(p), \ + (InterlockedCompareExchange((interlocked_val)(&(p)->value), \ + (newval), (oldval)) == (oldval))) +#endif +#endif + +#if defined(HAVE_ATOMIC_SOLARIS) +/* Solaris sparc & x86/64 */ +#include <atomic.h> +#define atomic_inc(env, p) \ + atomic_inc_uint_nv((volatile unsigned int *) &(p)->value) +#define atomic_dec(env, p) \ + atomic_dec_uint_nv((volatile unsigned int *) &(p)->value) +#define atomic_compare_exchange(env, p, oval, nval) \ + (atomic_cas_32((volatile unsigned int *) &(p)->value, \ + (oval), (nval)) == (oval)) +#endif + +#if defined(HAVE_ATOMIC_X86_GCC_ASSEMBLY) +/* x86/x86_64 gcc */ +#define atomic_inc(env, p) __atomic_inc(p) +#define atomic_dec(env, p) __atomic_dec(p) +#define atomic_compare_exchange(env, p, o, n) \ + __atomic_compare_exchange((p), (o), (n)) +static inline int __atomic_inc(db_atomic_t *p) +{ + int temp; + + temp = 1; + __asm__ __volatile__("lock; xadd %0, (%1)" + : "+r"(temp) + : "r"(p)); + return (temp + 1); +} + +static inline int __atomic_dec(db_atomic_t *p) +{ + int temp; + + temp = -1; + __asm__ __volatile__("lock; xadd %0, (%1)" + : "+r"(temp) + : "r"(p)); + return (temp - 1); +} + +/* + * x86/gcc Compare exchange for shared latches. i486+ + * Returns 1 for success, 0 for failure + * + * GCC 4.1+ has an equivalent __sync_bool_compare_and_swap() as well as + * __sync_val_compare_and_swap() which returns the value read from *dest + * http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html + * which configure could be changed to use. + */ +static inline int __atomic_compare_exchange( + db_atomic_t *p, atomic_value_t oldval, atomic_value_t newval) +{ + atomic_value_t was; + + if (p->value != oldval) /* check without expensive cache line locking */ + return 0; + __asm__ __volatile__("lock; cmpxchgl %1, (%2);" + :"=a"(was) + :"r"(newval), "r"(p), "a"(oldval) + :"memory", "cc"); + return (was == oldval); +} +#endif + +#else +/* + * No native hardware support for atomic increment, decrement, and + * compare-exchange. Emulate them when mutexes are supported; + * do them without concern for atomicity when no mutexes. + */ +#ifndef HAVE_MUTEX_SUPPORT +/* + * These minimal versions are correct to use only for single-threaded, + * single-process environments. + */ +#define atomic_inc(env, p) (++(p)->value) +#define atomic_dec(env, p) (--(p)->value) +#define atomic_compare_exchange(env, p, oldval, newval) \ + (DB_ASSERT(env, atomic_read(p) == (oldval)), \ + atomic_init(p, (newval)), 1) +#else +#define atomic_inc(env, p) __atomic_inc(env, p) +#define atomic_dec(env, p) __atomic_dec(env, p) +#endif +#endif + +#if defined(__cplusplus) +} +#endif + +#endif /* !_DB_ATOMIC_H_ */ |